Reactance system



Oct. 31, 1944. H. M. BACH 2,361,731

REACTANCE SYSTEM Filed Dec. 12, 1940 2 Sheets-Sheet l 17 n INVENTOR u v BY j L 2/ flaq ATTO RNEY H. M. BACH Oct.31, 1944.

REACTANCE SYSTEM Filed Dec. 12, 1940 2 Sheets-Sheet 2 Mixer 36 RFAmpL ZM w ATTORNEY Patented Oct. 31, 1944 Henry M. Bach, Woodmere, 35., assignor, by

mesne assignments, to Patents Research CorporatiomNew York, N. Yea-corporation ofiNew York Application December 12, 1940, Serial No. 369,701

8 Claims.

The present .invention relates to tuning control systems for oscillatory circuits embodying a reactance control discharge tube for varying the tuning or resonant frequency of the circuit in accordance with an electric controlling poten-- tial or current.

In particular, the invention is concerned with electrical oscillators of the self-excited type embodying a composite oscillator and reactance control tube, "wherein the oscillating frequency may be controlled in an easy and efiicient manner in accordance with a varying electrical bias potential applied to said tube.

An object of the invention is therefore to provide a system for controlling the resonant frequency of an oscillatory circuit utilizing an electron discharge tube performing the function both of an amplifier and reactance control element.

Another object is to provide a self-excited electrical oscillator circuit utilizing a single electron discharge tube serving both as an oscillating element and a reactance control device for varying the frequency of the oscillations.

There has been in the past a wide usage of circuits embodying a reactance control tube capable of controlling r varying the resonant "frequency of a tuned circuit in a purely electrical manner by varying a bias potential applied to said tube. Thus, in automatic frequency control systems provided in superheterodyne radio receivers the prob-lem'arises of effecting a variation of the local oscillator frequency as a function of the sense and magnitude of a direct current potential developed by a frequency discriniinator. Likewise, in the field of phase or frequency modulation the problem arises of modulating the frequency of a self-excited oscillator in accordance with the amplitude changes of an audio or other modulating signal wave. In these and other cases in the art a special reactance control tube is utilized 'which in fact constitutes an amplifier excited by a quadrature potential derived from currents flowing in the resonant circuit to be controlled and supplying an amplified quadrature voltage which is developed across said resonant "circuit thereby' to vary its apparent or virtual reactance.

The amount of quadrature current injected into the resonant circuit is varied by controlling the transconductance of the reactance tube in accordance with an electric bias potential applied to a control grid resulting in a variation of the apparent reactance and in turn of the virtual tuning adjustment of the resonant circuit. The 05 tron discharge tube quadrature control potential for the reaotance tube is produced by a suitable phase shifting means associated with the resonant circuit.

The present invention provides a new and improved electronic reactance circuit of thelabove general type utilizing a single electrondischarge path as an effective element for both an oscillator or amplifier and a variable re'ac'tance device whose virtual impedance determinative of the tuning or oscillating frequency may be varied over --subs'tantia1 limits by means or a direct current control potential.

A further object of the invention is to provide an oscillator-modulator which sin'rp'le in. de

sign and-requires a minimuim of parts :and circuit elements so as to be suitable especially in :small portable :or mobile phase or frequency modulated transmitters.-

Still a further? obje'c't is to provide a combined amplifier and/or oscillator and reactance control circuit, wherein atsin'gle electron discharge path performs" partly the :functions of the oscillator or amplifier, tuning'reactance as well as phase shifting means for effecting the ireactance control.

The above and further objects :and novel :aspects of the invention will become more apparent as the following description proceeds takenwith reference to the accompanying drawings forming part of this specification and wherein:

Figure 1 :showsaself-excited oscillator circuit embodying the principles or theiinvention wherein a special phase shifting network is provided -f or producing reactive oscillating current :for the control of the effective oscillatmg' frequency,

Figure 2 shows :a tuned amplifying circuit embodying .the principles for the invention,

Figures 3 to -a/r e modifications of oscillating circuits of the type shown in figure 11,

Figures 6-9 show modifications of circuits according to the invention wherein a .single elecis utilized to perform the function of both oscillator, variable vreactance,

and phase shifting means for controlling the oscillating frequencyin a purely electrical manner,.and-

Figure in :is a block diagram of a radio receiver embodying a composite :oscil lator-reactance con- ;trol tube according to the invention for automatic tuning or frequency control.

Like reference numerals identify like parts throughout the different views of the drawings.

With the aforementioned objects in view the present invention contemplates the utilization or discharge tube grid l4 and the anode l5.

perimposed upon the normal oscillations of the system and resulting in control of the virtual or effective oscillation frequency. The magnitude of the quadrature oscillating component is varied in accordance with a suitable control potential providing a variable a corresponding variation of the tuning 'or oscillation frequency.

Referring to Figure 1, there is shown a basic oscillatory circuit embodying the principles of the invention. This circuit utilizes an electron ID, in the example shown f the hexode type comprising the following electrodes arranged in the order named: a cathode H, a first control grid l2, a screen grid M, a second control grid l3, and an anode or plate l5. An additional suppressor grid connected to ground or cathode may be provided between the screen The cathode ll, first grid l2 and the screen grid l4 used as an anode in conjunction with an oscillatory or tank circuit comprisinginductance l6 shunted by a variable condenser 11 form a regenerative oscillator of the modified Hartley type wherein the screen grid is operated at zero radio frequency potential and the cathode H and control grid l2 are operated above ground or any other zero reference point of the circuit at radio frequency potentials. The direct current potential applied to the screen grid M as indicated by the sign supplies the power for generating and sustaining the oscillations in the oscillatory tank circuit frequencycr the oscillations .is determined substantially by the values of the inductance l6 and the capacity l1. Item 2!) represents the conventional grid blocking condenser and 2| a grid leak resistance for producing suitable ,bias potential for the grid l2 in a manner well understood.

Alternating or oscillating .voltage developed across the inductance I6 is impressed upon a phase shifting network comprising in the example shown a resistance 22 and a reactive impedance such as a condenser 23 connected in series therewith. The potential developed across condenser 23 is impressed upon the second control grid l3 by way of condenser 24 of large capacity. The constants of the resistance 22 and condenser 23 of the phase shifting network are so chosen that the potential applied to grid l3 by way of the capacity 24 which serves to block the direct current upon this grid from the phase shifting network is in quadrature with the oscillating voltage applied to grid l2 from tank circuit l6, l1.

.It can be shown in a tube of the type illustrated or in general in any electron discharge tube having a pair of control grids and a positively biased screen grid interposed between said control grids, that the plate current will be determined substantially by the following theoretical equation:

wherein er and eg represent the alternating voltages applied to the control grids, I0 is the steady bias for said tube to'effect ing system of a radio receiver or the or quiescent plate current and in, R2, 163 are constants depending on the characteristics of the particular tube used.

In the case of Figure 1:

Hence, the above equation may be written as follows:

p I kqA sin wt+k A cos wt a b c k A A sin wt cos wt which is apart of the total cathode current of.

the tube contains a reactance term (1)) of the plate current by which is meant a quadrature oscillating current with respect to the normal oscillating current. Due to the tapping of the cathode I2 from the inductance IE or the oscil latory tank circuit this term of the plate current and hence of the cathode current will be developed across the lower portion of the oscillating inductance l6 and if varied in its magnitude will have the effect of a variable reactance shunted across the oscillating tank coil. Thus, by varying the direct current bias on the grid [3 by the provision or a suitable biasing or control source connected to the terminals (1., b the control by this grid may be varied which will have the effect of varying the constant kz i. e. in turn the value of the quadrature oscillating current and the equivalent virtual reactance of the oscillating tank circuit. The bias for the grid [3 may be supplied e. g. by the AFC Voltage produced by the discriminator in an automatic tunbias voltage may represent the output of a microphone or other modulating circuit of a phase or frequency modulated transmitter. The bias potential is applied to the grid l3 through a high frequency choke coil or a high ohmic resistance as shown in Figs. 2, 3 and 7 to 10 or in any other suitable manner in order not to short circuit the radio frequency potential on grid l3 to ground through the biasing source.

From the foregoing it is seen that in a system proposed by the invention a single electron discharge stream is utilized both as an oscillating element for a self-excited oscillator as well as a reactance control path for controlling the oscil lation frequency as distinguished from the prior art arrangements requiring separate oscillator and reactance control devices. It will be evident, however, that the invention is not limited to oscillators and means to control the frequency thereof in the manner described, but that the novel principle can be applied with equal advantage to a tuned amplifier stage for electrically adjusting or controlling the tuning or alignmentof the amplifier.

A circuit of this type is shown in Figure 2.

In the latter, an oscillatory input voltage is impressed minals ase msi onant'circuit 11' in the plate circuit of the tube is' applied to output terminals e-.j inductively or in any other suitable manner. potential derived from the phase shifting net- Quadrature way of terminals a-b and via .a low-pass .filter comprising a pair of series resistors t9 and 2.0

and a shunt condenser l9. In this manner the circuit may be adjusted or aligned to the proper ,peak or resonance point. By using several tubes in cascade, tuning may be effected :by -:a single control voltage simultaneously biasing all the tubes, thereby eliminating the problem of ganging and aligning a number of mechanically coupled tuning elements.

Figure 3 shows an oscillator circuit similar to that according to Figure l utilizing a discharge tube of the pentagrid converter type comprising a further positive or anode grid 12' located between the .control grid l2 and screen grid M. The anode grid I2 in this case is regeneratively coupled with the oscillating tank circuit l6, l1 through a tickler coil I8 to form a self-excited regenerative oscillator system associated with the lower portion of the electron discharge path of the tube. The remaining portion of the electron discharge path serves as an amplifier for the quadrature or tuning control potential derived :from the oscillator tank circuit by means of the phase shifting network 22., 23 and impressed upon the control grid l3 by way of condenser 24 of large capacity. The amplified quadrature current developed in the plate circuit and controlled in accordance with the bias voltage on the grid l'3 derived from a control source connected to w-b is suitably fed back upon the oscillator circuit I6, I 1 such as through the tickler coil 18 by directly connecting the plate I 5 with the oscillating grid I2 as shown. The screen grid l4 in this case serves to prevent interaction between the'oscillating and amplifying (reactance) path of the tube.

The circuit shown in Figure 4 is similar to Figure 3 but utilizes a hexode type electron tube in place of a pentagrid converter wherein the functions of the grids l2 and I3 are interchanged, that is the oscillating system comprising tank circuit l6, l1 and the tickler coil [8 are connected to the grid l3'and plate l5 while the quadrature potential derived from the tank circuit is impressedupon the grid l2. In such an arrangement the normal and quadrature oscillating currents are superimposed or coupled through the electron stream compared with the physical coupling through the tank circuit in the case of Figures 1 and 3.

Figure 5 shows a modification of the circuit according to Figure 4 utilizing a pentagrid converter type electron tube provided with an additional negative control grid l2 between grid l2 and screen M to produce amplified quadrature current in its output circuit including for this purpose suitable load impedance such 'asan ohmic resistance In. The amplified quadrature current controlled by the bias on grid I2 is electron stream coupled with the upper or oscillating discharge path of the tube resulting in eifioient controlling action and increased range of the frequency control of this circuit.

Referring to Figure, 6. there is shown. still -;a a further modification of an oscillator-reactance tube circuit accordin to the invention. tube utilized in this-embodiment is o'fthe .hexode type similar to that provided in Figure 1 butcomprising an additional (suppressor) control grid 'l3' arranged between the screen grid 14 and .plate l5; The oscillating tank circuit l6, l'land tick'ler coil 18 are connected to the grid l3" and plate l5 to form a regenerative oscillating system. The controlgrid I2 is excited in phase with the oscillating frequency bydirectlycoupling it to the tank circuit l6, l1 throughcouplingcondenser 25. Control grid I3 is operated at cathode potential or if desirable at a negative potential with respect to the cathode whereby this grid will be excited by a potential in phase quadrature .to the space current oscillations by space charge coupling with the grid 12 as will be further understoodirom the following. Electrons accelerated by the-screen grid 14 are attracted through the control grid. 12 and will partly pass the openings of the screen grid to be slowed down or repelled by the decelerating action of grid H which is at a substantially negative potential with respect to the screen grid l4. As a result of this decelerating action a concentrated electron space charge or virtual cathode will be formed within the space between the screen grid l4 and control grid [3. The intensity of this virtual cathode varies in the rhythm of the space current variation i. e. the same as control potential applied to the grid 12. The variable space charge or virtual cathode causes a corresponding current to flow through the outer circuit connected to grid 1 3 and including a non-reactive impedance such as resistance 26 which current being a displacement current will be in phase quadrature to the fluctuations of .the virtual cathode, that is in turn to the potential upon the grid I'2. As a result thereof a potential will be developed on grid I3 which is in phase quadrature to the potential on the oscillating control grid l3. In this manners quadrature or reactive current component due to the control action of grid .13 will be superimposed upon the normal oscillating current in the output circuit of the tube. resulting in a variation of the eifective'tuning in accordance with a direct current biasing potential applied to the controlgrid l2 from an AFC circuit or any other biasing or controlling source. It is seen therefore that in a circuit ac cording to Figure :6 a single electron discharge path is utilized as an efiective element in performing the function of both oscillatoras well as phase shifting and reactance control means in a most simple and efiicient manner.

Figure 7 shows a modification of a combined oscillator-reactance control circuit utilizing a virtual cathode or space charge coupling for producing a reactance or frequency control component of the total oscillating current. The discharge tube utilized is similar to that shown in Figure 1. Grid l3 of this tube is excited in phase from the tank circuit I6, I 'l by way of blocking condenser 30. The plate I5 is grounded to serve as a decelerating electrode so as to develop a quadrature potential in the cathode-plate path that is across the bottom part of the tank circuit inductance l6 by virtue of the capacitative coupling of the plate IS with the space charge or virtual cathode formed between the screen grid l4 and plate IS. The reactance and frequency control is eifected by varying the bias potential on the grid l3 resulting in a corresponding var-la- The *tion of the intensity of the virtual cathodeand tube shown in Figure 1.

, stood from the foregoing.

in turn of the reactive control voltage developed across the oscillatingtank circuit. The control potential in the example shown is supplied by the secondary of an audio frequency transformer 21 having its primary connected to a source of direct current 28 in series With a microphone 29 or equivalent control element. The source 28 simultaneously serves to supply constant negative bias for the grid l3 to ensure most favorable operating conditions. In this manner frequency modulated oscillations may be derived from the tank circuit l6, l1 exciting an antenna or other transmission circuit by Way of an amplifier connected to terminals cd or alternative- -ly for exciting a frequency multiplier to increase the frequency deviation to an extent required in wide band frequency modulation. Similarly, the circuit may be employed as a phase modulator' in which case a suitable corrective network may be inserted between the microphone circuit and the tube to increase the control potential directly in proportion to the modulating frequency so as to obtain modulated oscillations having a phase deviation proportional'only to the.

amplitude of the modulating signals. 1

Figure 8 shows another circuit utilizing a variable space charge or virtual cathode for pro.- ducing a quadrature oscillating component. The tube used is of the pentode type similar to the The oscillating system 16, ll, [8 is operatively connected to the control grid l3 and anode [5. Grid I2 connected to the biasing source is operatedat cathode or negative potential and accordingly will be excited by a potential in phase quadrature with the space current oscillations due to variable space charge coupling with the electron stream. This coupling is due to the space charge formed, between the grid l2 and the screen l4, by electrons which after passing the screen [4 and deceleration byv the grid l3 are returned so as to pass the screengrid M in the opposite direction and become finally decelerated by the grid l2 toform a second space .charge or virtual cathode adjacent to the latter in addition to a first virtual cathode formed 'by other electrons between the screen l4 and grid 13 as described hereinabove. The excitation of grid 12 in quadrature to the space current oscillations ;will cause a corresponding quadrature oscillating component in the output circuit which in turn will result in a variation of the effective or virtual tuning or control of the oscillating frequency in substantially the same manner as in the preceding circuits.

Referring to Figure 9 there is shown a circuit similar to Figure 8 wherein the functions of the grids l2 and 13 have been interchanged, thatis the oscillatory system l6, l1, IB is associated with the grid [2 and theplate l5, while the grid I3 is space charge excited in quadrature .with the oscillatingspace current by the virtual cathode formed between the screen I l and the grid l3 as under- In Figure there is shown a circuit, partly in block diagram form, of a superheterodyne radio receiver embodying a composite oscillator-reactance tube circuit in accordance with the invention for effecting automatic frequency or tuning adjustment. Radio signal waves intercepted by the antenna are impressed upon a radio frequency amplifier by way of a coupling transformer 36. The amplified radio frequency signals are then applied to a first decondenser 43.

cillator is of the type as shown in Figure 1 comprising a vacuum tube ID with an oscillating and reactance control system associated therewith for controlling the frequency of the oscillating potential impressed upon the mixer 38 by way of The adjustable tuning members of the radio frequency amplifier, the mixer and "local oscillator are suitably coupled mechanically as indicated by dotted lines 44 for uni-control of the receiver in a manner well known. A fraction of the intermediate frequency signal energy is applied upon a discriminator 42 of any suitable type known in the art and adapted 'to produce a control potential varying both in sense and magnitude independence upon and in proportion to the'deviation of the intermediate signal frequency from the assigned center frequency of the resonance characteristic of the intermediate frequency amplifier 39. The discriminating potential is impressed upon the grid [3 of the oscillator-reactance tube with such polarity that the ensuing variations of the oscillating frequency will counteract the initial frequency deviation of the intermediate frequency signal from the assigned frequency in such a manner as to bring about or maintain the receiver in exact tuning adjustment.

It will be evident from the foregoing that the invention is not limited to the specific details and circuit arrangements described and disclosed herein for illustration but that the underlying idea and principle of the invention are susceptible of numerous variations and modifications coming within the broader scope and spirit of the invention as defined in the appended claims. The

specification and drawings are accordingly to be regarded in an illustrative rather than a limiting sense.

I claim:

1. In combination, a circuit traversed by alternating current, an electron discharge device comprising a cathode and an anode, a first control grid near said anode and a second control grid near said cathode, means for impressing alternating potential from said circuit upon said first grid, phase shifting means consisting of space charge coupling within said device for applying alternating potential from said circuit to said second grid substantially in phase quadrature to the potential upon said first grid, a sourceof variable potential arranged to controlthe bias of said second grid, and an output circuit operatively connected to said anode.

2. In combination, a circuit traversed by alternating current, an electron discharge device comprising a cathode and an anode, a first control grid near said anode, a second control grid near said cathode, and a screen grid at zero alternating potential arranged between said first and second control grids, means for impressing alternating potential from said circuit upon said first control grid, phase shifting means consisting of space charge coupling within said device for applying alternating potential from said circult to said second control grid in substantially phase quadrature relation to the potential upon said first grid, a source of variable bias poten tial connected to said second grid, and an output circuit operatively connected to said anode.

3. A self-excited oscillator comprising an electron discharge tube having main input and output electrodes and a resonant oscillatory circuit coupled thereto in regenerative circuit arrangement to generate sustained electrical oscillations, at least one further control electrode within said tube effective in controlling the current in said circuit, phase shifting means consisting of space charge coupling within said tube for applying quadrature oscillating potential from said circuit to said control electrode to produce a quadrature oscillating current with respect to and superimposed upon the main oscillating current in said circuit, and a source of variable potential arranged to control 'said quadrature current to correspondingly vary the efiective frequency of the oscillations produced.

4. A self-excited oscillator comprising an electron discharge tube having main input and output electrodes and a resonant oscillatory circuit coupled thereto in regenerative circuit arrangement to generate sustained electrical oscillations, at least one further control electrode within said tube effective in controlling the current in said oscillatory circuit, a screen grid at zero oscillating potential arranged to prevent direct reaction between the oscillator circuit and said control electrode, phase shifting means consisting of space charge coupling within said tube for impressing quadrature oscillating potential from said circuit to said control electrode to produce a quadrature oscillating current with respect to and superimposed upon the main oscillating current in said circuit, and a source of variable potential arranged to control said quadrature current to correspondingly vary the frequency of the oscillation produced.

5. A self-excited oscillator comprising an electron discharge tube having a cathode and an anode, a first control grid near said anode and a second control grid near said cathode, a resonant oscillatory circuit connected to said first grid and anode in regenerative circuit arrangement to generate sustained electrical oscillations, phase shifting means consisting of space charge coupling within said tube for impressing a phase-shifted oscillating potential from said circuit upon said second grid to produce a phaseshifted oscillating current with respect to and superimposed upon the main oscillating current in said circuit, said phase shift being of the order of ninety degrees, and a source of variable coupling within said device acting as phase shifting means for impressing alternating potential from said circuit upon the other of said grids in predetermined phase relation with respect to the potential upon said first grid to cause a phaseshifted current component with respect to and Superimposed upon the main alternating current in said circuit, said phase shift being of the order of ninety degrees, a source of variable control potential arranged to control said phaseshifted component, and an output circuit operatively connected to said anode.

'7. In combination, a circuit traversed by alternating current, an electron discharge device comprising a cathode, an anode and a pair of control grids each being efiective in controlling the space current to said anode, a screen grid at zero alternating potential arranged between said control grids, means for impressing alternating potential from said circuit upon one of said control grids, solely space charge coupling within said device acting as phase shifting means for producing phase-shifted alternating potential upon the other of said grids to cause a phaseshifted current component with respect to and superimposed upon the main alternating current in said circuit, said phase shift being of the order of ninety degrees, a source of variable control potential arranged to control said phase-shifted component, and an output current operatively connected to said anode.

8. A self-excited oscillator comprising an electron discharge tube having a cathode, an anode, a first control grid near said anode, a second control grid near said cathode, a third control grid between said first and second control grids, and an acceleration grid between said second and third control grids, a resonant oscillatory circuit connected to said first control grid and anode in regenerative circuit relation to generate sustained electrical oscillations, means for impressing oscillating potential from said circuit to said second control grid, a substantially non-reactive impedance connecting said third control grid to said cathode, and a source of variable control potential connected to said second control grid.

HENRY M. BACH. 

